Rafael Nadal has withdrawn from the Asian leg of the ATP Tour as he continues to recover from a knee injury sustained at the US Open.

World No. 1 Nadal announced he had visited doctors in Barcelona to treat the discomfort in his right knee that forced him to retire during the semifinal against Argentine Juan Martin del Potro at Flushing Meadows earlier in September.

The Spaniard, 32, has decided not to play the China Open in Beijing -- scheduled for the first week of October -- or the Shanghai Masters a week later, leaving the door open for Novak Djokovic to move top of the world rankings by the end of the year.

Maria Sharapova has withdrawn from her final three events of the 2018 season in order to focus on getting her right shoulder healthy for next year. Her first event of the 2019 season is expected to be the Shenzhen Open.

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"We decided together with my medical and technical team not to participate in the Asian tour to recover the knee in the way we have always done," Nadal tweeted.

"I regret not being able to be with all the many fans in China and with the organisers of the Beijing and Shanghai tournaments who have always been so kind to me and my team."

The 17-time Grand Slam champion has enjoyed an impressive year, winning the French Open for the 11th time and sealing victories at the Monte Carlo Masters, Italian Open and Canadian Open.

But Djokovic is now primed to snatch Nadal's No. 1 ranking after a magnificent summer saw him win at Wimbledon and defeat del Potro in the US Open final.

Nadal currently leads the way with 8,760 points, 1,860 ahead of Roger Federer -- who is limiting the number of tournaments he plays in -- and 2,315 clear of Djokovic.

The Serbian can only gain points in the Far East because he missed the final six months of last season, while Nadal will drop points for not defending his title in Beijing or participating in Shanghai.

The decision will not impact Nadal's qualification for the end of season ATP World Tour Finals in November because he has already ensured his participation at the O2 Arena in London.

Top spot could then be decided at the Paris Masters at the end of October -- the final Masters event before the World Tour finals.